二维模型优化ZnO金属-半导体-金属光探测器特性

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本文主要探讨了理论优化金属-半导体-金属(ZnO)光电探测器（MSM PD）的特性。研究者通过开发了一个二维模型，将金属-半导体-金属结构的基础建立在半导体的漂移扩散模型之上。这个模型能够精确地计算结构内部的电势分布、横向和纵向的电场分布，以及载流子浓度分布，从而深入理解光探测器的工作原理。模型的核心是利用半导体的物理特性，如能带结构和载流子迁移率，来模拟光吸收后的载流子运动和扩散过程。通过这种方式，作者得以评估不同结构参数，如手指间距(s)和手指宽度(w)对暗电流的影响。暗电流是衡量光电探测器性能的重要指标，它反映了没有光照时器件的电流噪声，对提高探测器的信噪比至关重要。研究结果显示，通过对这些关键参数进行优化，可以显著降低暗电流，从而提升MSM ZnO PD的灵敏度和响应速度。实验数据与理论计算结果高度吻合，证实了模型的有效性。这一工作对于设计和改进高性能ZnO基光电探测器具有重要的指导意义，特别是在光通信、光传感和光电子设备领域，尤其是在微型化和集成化的趋势下，对减小尺寸、降低成本和提高效率的要求日益迫切。此外，文章还强调了接触区的欧姆特性验证，这是确保良好光电转换的关键因素，良好的接触有助于减少接触电阻，进一步提高探测器的性能。这篇论文提供了一种理论框架，使得科研人员能够在设计ZnO MSM PD时有目标地优化其关键参数，从而实现更高效的光探测性能。

COL 9(10), 100401(2011) CHINESE OPTICS LETTERS October 10, 2011

Theoretical optimization of the characteristics of ZnO

metal-semiconductor-metal photodetectors

Ghania Harzallah

∗

and Mohamed Remram

Lemeamed Laboratory, Department of Electronics, University of Mentouri Constantine, Algeria

∗

Corresponding author: ghan harzallah@yahoo.fr

Received December 20, 2010; accepted March 15, 2011; posted online July 11, 2011

A two-dimensional model of a metal-semiconductor-metal (MSM) ZnO-based photodetector (PD) is devel-

oped . The PD is based on a drift diffusion model of a semiconductor that allows the calculation of potential

distribution inside the structure, the transversal and longitudinal distributions of the electric field, and the

distribution of carrier concentration. The ohmicity of the contact has been confirmed. The dark current

of MSM PD based ZnO for different structural dimensions are likewise calculated. The calculations are

comparable with the experimental results. Therefore, the inﬂuence with resp ect to parameters s (finger

spacing) and w (finger width) is studied, which results in the optimization of these parameters. The best

optimization found to concur with the experimental results is s = 16 µm, w = 16 µm, l = 250 µm,

L = 350 µm, where l is the finger length and L is the length of the structure. This optimization provides

a simulated dark current eq ual to 24.5 nA at the polarization of 3 V.

OCIS codes: 040.5160, 250.0250, 160.6000.

doi: 10.3788/COL201109.100401.

Extremely complex, integrated photonic c ircuits are de-

veloped and industrially produced. This is in consid-

eration of the demand for low-cost high-bandwidth cir-

cuits, and the demand for knowledge control regard-

ing the manufacturing processes of semiconductor opto-

electronic components. The metal-semiconductor-metal

(MSM) photodetector (PD) is a good choice in the photo

detection field due to the simplicity of manufacture and

suitability for monolithic integration

[1,2]

. Indeed, the

planar structure of MSM PD results in an exception-

ally small capacity, which is highly desired for high-

bandwidth and low-noise performance

[3]

. Recently, gen-

eral manufacture of MSM PD used semiconductor ma-

terials with wide and direct gaps. The ZnO with direct

gap (3.3 eV) has attracted considerable interest becaus e

of its excellent electrical properties that allow wide appli-

cation in high temperatures and high pressures, as well

as in the fabrication of components needed to addres s

very high response time

[4,5]

. Furthermore, ZnO has high

sensitivity in ultra- violet detection, making it one of the

detectors popularly used for monitoring air quality and

gas detection, as well as in military applications

[6−8]

In recent ye ars, a significant number of studies have fo-

cused on the MSM PD based ZnO, using different met-

als for interdigitated contacts. Majority of these stud-

ies were experimental

[9−11]

, with only a few fo c using on

the theore tical aspect. The model construction is impor-

tant in understanding a certain number of physical phe-

nomena that may be difficult to achieve experimentally

because of the high cost and time requirement, par ticu-

larly those of advanced technologies. Controlling trans-

port phenomena in MSM PDs by modelling with nu-

merical methods is especially important in the present

case becaus e specific materials such as undoped ZnO are

used. O ther researchers have developed the subject using

simulators, such as COSMOL multiphysics

[12,13]

. In the

present work, a two-dimensional (2 D) theoretical mo del

of a MSM-PD-based ZnO is develope d, with aluminum

as the interdigitated metal contact. The dark current is a

point of interest because it provides important electrical

properties such as the direct reﬂection of PD sensitivity.

A number of different dimensions of the MSM structure

are used to calculate the current. The results are inter-

preted and discussed to provide an optimum geometry in

obtaining a minimum dark current. A comparison with

exp erimental results is performed.

The MSM PD consists of two interpenetrating metal

contacts in the form of an interdigitated comb; one is

forward biased and the other is reversed biased. The free

surface o f the semiconductor between the two contacts is

the active area for absorbing light for photocurrent gener-

ation. Command and control of the electric conduction

mechanism make it possible to minimize the dark cur-

rent. Thus, the conception of a proper design for MSM

PD which can detect even the lowest electrical p ower is

possible. The basic layout of the planar MSM PD for

simulation is given in Fig. 1.

The metal-semiconductor contacts can be ohmic o r

Schottky depending on the value of metal work function

and the value of the semiconductor aﬃnity. Consider-

ing the geometrical symmetry of interdigitated electrodes

and facility of calculation, only a unit ce ll was considered,

in which the unit cell lateral boundaries are found in the

middle o f two adjacent electrodes (Fig. 2).

The proposed model is a 2D physical drift diffusion

model based on the Poisson equation, co ntinuity equa -

tions, and equa tions of currents. The expressions are

ε∇

ψ = −q(p − n + N

), (1)

= qµ

nE + qD

∇

, (2)

= qµ

pE − qD

∇

, (3)

∂n

∂t

∇ · J

− R + G

opt

, (4)

1671-7694/2011/100401(5) 100401-1

 2011 Chinese Optics Letters

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